1. The Field of the Invention
The present invention relates to authentication credentials. More specifically, the present invention relates to methods, systems, and computer program products for authenticating a mobile client that may have an input system optimized for numeric input.
2. Background and Related Art
Content stored on networks often is protected for a number of reasons. For example, content may include proprietary technology that provides a business with a competitive advantage. Many employers consider at least some portion of their personnel information private or confidential. It may be important to protect certain vital content, such as customer orders, from corruption or loss. Whether the motivation is to insure confidentiality or privacy, to prevent the corruption or loss of content, or to secure sensitive information, access to computer networks usually is governed through authentication credentials, such as a username and password for a particular system or domain.
However, authentication credentials for a computer network may be compromised in a number of ways, including brute force attacks, monitoring network traffic, and gaining access to third-party systems that store authentication credentials. In a brute force attack, a large number of potential authentication credentials, perhaps all possible combinations, are submitted to a computer network. For example, a four-digit PIN (personal identification number) could be discovered by submitting the numbers from 0000 to 9999. Although submitting ten thousand numbers may seem like a significant task, for computers the imposition is minimal at best.
A common defense to brute force attacks is to increase the number of possibilities that must be submitted. Each added digit increases the number of potential selections by a factor of ten. If letters are available in addition to numbers, each character represents a factor of thirty-six. Including upper and lower case letter increases the weight of each character to sixty-two. For maximum protection, punctuation may be added to numbers and letters, arriving at a familiar one hundred and one possible choices for each character. (Typical English keyboards sold in the United States are described as 101 keyboards, indicating the number of printable characters that are supported.) Even if some characters are not allowed, with about one hundred options for each of four characters, the number of distinct combinations approaches 100 million, a significant improvement over the ten thousand combinations offered by a four-digit PIN.
Because arbitrary combinations of numbers, letters, and punctuation are difficult to remember, words, dates, acronyms, and the like, may help to keep authentication credentials familiar. Attackers exploit this weakness by employing a type of brute force attack, typically known as a dictionary attack. There is no need to try all combinations of letters or numbers; rather, only combinations that make sense as words, acronyms, or dates are submitted. Limiting the attack to a “dictionary” may reduce our 100 million improvement back to the range of ten or twenty thousand, and even less if only relatively common words are considered.
To reduce the threat posed by dictionary attacks, network administrators may impose policies regarding authentication credentials. For example, passwords may be required to include at least one upper case letter, at least one lower case letter, at least one number, and at least one punctuation character. In addition, a certain length may be mandated, such as five, six, seven, or eight characters. Because long passwords are more difficult to remember, specifying much more than eight characters may be counter productive because the passwords will be written down rather than memorized, allowing for authentication credentials to be compromised if the written password is ever discovered. For example, an all too common occurrence in a financial context is storing a PIN with its corresponding charge or debit card. Any value to the PIN is all but lost if the PIN must be written to be remembered. Similar issues exist in other environments, particularly regarding access to computer networks.
Recently, there has been an increasing demand for access to computer networks, and the content they may offer, using mobile clients. Due to their convenient size and utility, telephones are among of the most widely-used mobile clients. However, some mobile clients, such as telephones, have input systems that are optimized for numeric input. While letters and punctuation may be available, it is often quite cumbersome for most users to enter any characters other than numbers. As described above, allowing authentication credentials that only contain digits makes a computer network vulnerable to brute force attacks.
Furthermore, third parties may be involved in providing mobile access to content. For example, telephones may connect to a wireless application protocol (“WAP”) server in reaching a desired network or content server. In many circumstances, the WAP server and the network will be entirely unrelated. Businesses may be unwilling or unable to bear the expense of offering mobile access to their network, whereas telephone carriers will be able to use WAP servers as a revenue stream through increased airtime.
Intermediate servers represent a security risk, because wireless protocols may not provide for secure end-to-end connections. Secure connections may be limited to each hop, such as a secure connection between a telephone and a WAP server, and a secure connection between the WAP server and the network being accessed. As a result, the WAP server will contain unencrypted content. For example, the telephone may enter authentication credentials that are encrypted during transit to the WAP server. The WAP server decrypts the authentication credentials and then re-encrypts the authentication credentials based on the secure protocol used in communicating with the network. If the WAP server is compromised, an attacker may be able to acquire authentication credentials that will allow access to any network that the mobile clients have accessed. Furthermore, to reduce the amount of information that must be remembered, mobile clients may use the same authentication credentials for other networks that do not provide mobile access, making those other networks vulnerable to attack as well.
Although it may be unlikely that an intermediate server will be compromised, the problem for the network is that the risk may be difficult to quantify. Security measures at the intermediate server are determined, implemented, monitored, and controlled, by whomever is responsible for the intermediate server. For some networks, the risk from numeric authentication credentials, coupled with uncertainty as to the extent of security provided by an intermediate server, will be too great, and mobile access will be prohibited.